So I found a great deal on nugs and picked up a 142 and 146 due to being unsure about weight concerns. I'm typically 170 and the 142 shows 170 as the upper end and the 146 has 180. Anyone around my weight that can offer their experience on either size? I'd follow the 8-10cm guideline but my current decks are 152(park), 155 (all mt) 158 (pow) and 163 (big mt). I'm leaning toward the 156 and just want to make sure I won't miss out by not going 146

I dont weigh as much as you but I would probably pick the the 146. With both your weight and regarding the 8-10cm downsizing, you'd be at the max limits of that 142(using your 152 park board which is the smallest you have). So just with the Burton weight requirements you can see the 146 is a better choice and also using your All Mtn board(since the park/pow/big are more specialized sticks) dropping 9cm would put you at 146 which is right in the sweet spot of 8-10cm downsizing.

The 146 would put you in a sweet spot, not too small and not too big. I ride the 142 and I weigh 150lbs and my usual size is 150. So I'm on the lower end of the scale.